In order to protect an internal combustion engine from the deleterious effects of running at excessive speed it is desirable automatically to limit the maximum speed at which the engine can be operated. The maximum operating speed is selected according to the construction and operating characteristics of the engine so as to provide a useful range of operating speed while protecting the engine from the excessive wear and destructive stresses incident to excessive speed. Over the years, many different devices have been proposed for limiting the speed of internal combustion engines. However, such devices have not been found to be entirely satisfactory. Among the disadvantages of prior devices are complexity of construction, excessive size and weight, unreliability in operation and variation in control speed due to wear or different operating conditions.